1. Field of the Invention
The present invention relates to a shaft sealing apparatus used in hydraulic machineries such as water turbine, pump and so forth for preventing a fluid from leaking out from the working chamber of the hydraulic machine.
2. Description of the Prior Art
Generally, a hydraulic machine such as a water turbine, pump or the like incorporates an impeller attached to a rotary shaft which extends outside a stationary casing of the hydraulic machine so as to be operatively connected to, for example, a generator or a motor. A shaft sealing apparatus is provided in a portion between the stationary casing and the rotary shaft adjacent to the impeller to prevent the fluid of a high pressure in the working chamber of the hydraulic machine from leaking out through an annular gap defined by an outer surface of the rotary shaft and the stationary casing.
Various types of shaft sealing apparatus have been proposed for the hydraulic machines.
One of these known shaft sealing apparatus is so constituted that a seal ring fixed to the stationary casing is abutted against one axial end surface of a collar projecting radially outwardly from an outer periphery of the rotary shaft so as to form a fluid tight seal therebetween. This type of shaft sealing apparatus, however, suffers from the following problem. Namely, when this shaft sealing apparatus is used under a severe condition such as high pressure and high speed, the sliding surface of the seal ring is thermally damaged by a friction heat generated between the sliding surfaces of the seal ring and the collar, so that the seal ring is worn down rapidly and the sliding surface of the collar is also damaged soon. In addition, in the case of a hydraulic machine such as a water turbine which handles water containing sand and soil particles, there is a fear that the sand and soil particles may inconveniently flow into between the sliding surfaces to cause a rapid wear thereof.
In order to obviate this problem the "Water Power & Dam Construction" (February 1977, pp42-45) discloses a shaft sealing apparatus in which clean water is supplied between the sliding surfaces of the collar and the seal ring to not only cool them but also remove the sand and soil particles to prevent rapid wear thereof. It is, therefore, necessary that clean water be introduced to the sliding surfaces to eliminate the particles therefrom. However, the water to be supplied should be fresh, containing no sand and soil particles as well as, the supply of this fresh water has to be made at a sufficiently high pressure so that it may wedge into the gap between the sliding surfaces which are usually pressed to each other at a high pressure to seal the water of the high pressure in the hydraulic machine.